Field of the Invention
The present invention relates to a scintillator, a scintillator panel, and a radiological image conversion panel used at the time of forming a radiological image.
Description of the Related Art
In the related art, a radiological image such as an X-ray image is widely used to diagnose a medical state in medical sites. Particularly, a radiological image using a screen-film system has achieved both high image quality and high sensitivity in this long-time history, and as a result thereof, the radiological image is used in worldwide medical sites as an imaging system that has both high reliability and excellent cost performance. However, such image information is so-called analog image information, and free image processing and instantaneous electric transmission like digital image information currently continuously developed may not be performed.
Recently, digital-mode radiological image detectors represented by computed radiography (CR), a flat panel detector (FPD), and the like are newly released. In these radiological image detectors, a digital radiological image can be directly obtained, an image can be directly displayed on an image display device such as a panel utilizing a cathode tube, a liquid crystal panel, and the like, and convenience of diagnosis work in a hospital or a health clinic is significantly improved.
In the above-described FPD, in principle thereof, a scintillator panel including a phosphor (scintillator) layer made of an X-ray phosphor having characteristics to convert radiated X-rays to visible light and emit the visible light is used in order to convert the X-rays to the visible light. At this point, there may be problems in which luminance of the scintillator itself is reduced (also referred to a luminance “weakening”) due to long-time exposure to the X-rays and calibration is needed.
The inventors of the present invention consider that such problems are caused by influence of content of an augmenting agent.
As an example of using an augmenting agent together with a phosphor, an appropriate value of a Tl concentration inside a CsI/Tl phosphor layer is 0.38 to 1.91 wt % in JP 2012-098110 A, and JP 2012-098110 A discloses a fact that there is no difference observed in a sensitivity characteristics even when an average Tl concentration is set to 0.3 wt % which is lower compared to the Tl concentration in the related art.
Additionally, in JP 2008-051793 A, it is disclosed that a concentration of an augmenting agent is set high (0.7 mol % or more) on a radiation incidence side and set low (0.3 mol % or more) on a light detector side inside a scintillator layer formed of an aggregate of columnar crystals.
Furthermore, the applicant of the present application also proposes in JP 2015-017972 A that an augmenting agent concentration profile curve in a thickness direction of a scintillator layer has two or more peaks and an amount of the augmenting agent existing in a region up to the thickness of 100 μm from a main surface facing a photoelectric conversion element of the scintillator layer is 0.3 to 0.7 mol %.
There also is a Non-Patent Literature that refers to influence of content of an augmenting agent. For example, Jing, T., et al. of “Evaluation of a structured cesium iodide film for radiation imaging purposes.” Nuclear Science Symposium and Medical Imaging Conference in 1993, 1993 IEEE Conference Record, IEEE, 1994 states that a concentration of an augmenting agent (thallium) so as to have an optimal amount of luminescence is 0.1 to 0.2 mol %. Additionally, the same literature also states that the concentration should not be set to 0.02 mol % or less in order to have a favorable amount of luminescence, and discloses a fact that an extremely low concentration is rather not preferred.